In many well related operations, appropriate well equipment is moved downhole to control fluid flow. For example, various completions are used to facilitate and control the flow of fluid in both production operations and injection operations. Valves are sometimes used to choke or otherwise control flow of fluid through the well equipment.
In some applications, detrimental reverse flow can be a problem and valves have been used to prevent flow in the undesirable direction. Flapper valves, for example, have been used to enable flow through tubing in one direction while blocking flow in the opposite direction. However, flapper valves offer limited ability for adjustment to accommodate various procedures during a production and/or injection operation.
For example, many subsurface safety valves utilize a flapper as a closure mechanism fitted within a body or housing member to enable control over fluid flow through a primary longitudinal bore upon an appropriate signal from a control system. The signal typically is a rapid reduction of the hydraulic operating pressure that holds the valve open, thereby facilitating shut-in of the production or injection flow. The closure mechanism typically is movable between the full closed and full open positions by movement of a tubular device, often called a flow tube. The flow tube can be moved to the open position or operated by the valve actuator which is motivated by hydraulics, pressure, electronics, or other external signal and power sources. The shifting of the flow tube to a closed position typically is performed by a mechanical power spring and/or a pressurized accumulator that applies a required load to move the flow tube to the closed position upon interruption of the “opening” signal. As a result, the valve may occasionally be required to close against a moving flow stream in the performance of its designed function. However, this action can subject the valve to substantial loading forces.